The purpose of this project is to study the genetic activity of aflatoxins and their metabolites in the yeast Saccharomyces cerevisiae. The topics of present interest are: (1) Comparison of the genetic activity of aflatoxin B1 and G1 when metabolized by hamster liver homogenate; (2) An investigation of the metabolism of aflatoxin B1 by an alteration of epoxide hydrase activity with the inhibitor 1,2-epoxy-3,3,3-trichloropropane, and (3) Activation of aflatoxin B1 by yeast cells and a possible correlation with the cytochrome P-450 content of yeast.